diff --git a/pkg/util/net/dial.go b/pkg/util/net/dial.go
index 1a3859ed..b0a5e437 100644
--- a/pkg/util/net/dial.go
+++ b/pkg/util/net/dial.go
@@ -45,6 +45,11 @@ func DialHookWebsocket(protocol string, host string) libnet.AfterHookFunc {
 		if err != nil {
 			return nil, nil, err
 		}
+		// The tunnel payload is a raw byte stream (yamux), not UTF-8 text.
+		// Send it as binary frames; otherwise RFC 6455-compliant intermediaries
+		// (e.g. API gateways/reverse proxies) UTF-8-validate the default text
+		// frames and close the connection on invalid bytes.
+		conn.PayloadType = websocket.BinaryFrame
 		return ctx, conn, nil
 	}
 }
diff --git a/pkg/util/net/websocket.go b/pkg/util/net/websocket.go
index 6c2f39c4..57641b31 100644
--- a/pkg/util/net/websocket.go
+++ b/pkg/util/net/websocket.go
@@ -32,6 +32,11 @@ func NewWebsocketListener(ln net.Listener) (wl *WebsocketListener) {
 
 	muxer := http.NewServeMux()
 	muxer.Handle(FrpWebsocketPath, websocket.Handler(func(c *websocket.Conn) {
+		// The tunnel payload is a raw byte stream (yamux), not UTF-8 text.
+		// Send it as binary frames; otherwise RFC 6455-compliant intermediaries
+		// (e.g. API gateways/reverse proxies) UTF-8-validate the default text
+		// frames and close the connection on invalid bytes.
+		c.PayloadType = websocket.BinaryFrame
 		notifyCh := make(chan struct{})
 		conn := WrapCloseNotifyConn(c, func(_ error) {
 			close(notifyCh)